1. Field of the Invention
The present invention relates to a projection display such as a projection television and display. In particular, the present invention relates to a lens array sheet which is suitable for such a usage and a projection screen which uses such a lens array sheet.
It is possible to name a CRT, LCD (liquid crystal display device), DMD (Digital Micro-mirror Device; a trademark registered by Texas Instruments Corp.) for such a representative display such as a projection television in which an image which is emitted from a projector which is provided with various optical engine. In particular, a transparent (projection type, rear-projectiontype, rear type) projection television is representative.
Hereinafter, the present invention is explained for mainly a transparent projection screen.
2. Description of the Related Art
A screen is commonly known which is used for a projection television which is provided with a CRT projector having a structure shown in FIG. 10 for one of a conventional projection television screen.
Such a screen is provided with a lenticular sheet 320 which has concave sections and convex sections for forming lens sections on it both surfaces and two pieces of lens sheet member for a fresnel lens sheet 310 such that the lenticular sheet 320 is disposed nearer to an observing person than the fresnel lens sheet 310.
Also, there is a case in which a plane protecting board (not shown in drawings) may be disposed on an outermost position near the observing person.
The lenticular sheet 320 is formed by forming lens sections 322, 328 which are formed by disposing a plurality of cylindrical lens of which vertical direction is its longitudinal direction in a horizontal direction on both surfaces of the lenticular sheet 320. The lenticular sheet 320 has a lens section 328 for the observing person so as to adjust a color shift for an image light which is emitted from a three-tube projector which has colors such as R, G, and B by refracting and dispersing the image light and a lens section 322 near an emitting side compatibly. (Hereinafter, it may be called a double-surface lenticular sheet.)
It is common that the double-surface lenticular sheet 320 should be formed by an extruding method in which optical axes of the lens sections on both surfaces must be aligned.
On the other hand, not only a refracting and dispersing function in a horizontal direction by the above lens section (an image light is broadened in a horizontal direction by disposing the cylindrical lens group in the horizontal direction) but also a broadening function for the display image in also a vertical direction (enlarging a vertical perspective angle) are required in the projection screen.
An angle which is greater than 10 (ten) degree is required for a example for enlarging a vertical perspective angle (an angle which transmits from an orthogonal direction to a front surface-screen in a case in which a brightness of the displayed image light in the front surface may be reduced by a half when a viewpoint is moved from the front surface to an orthogonal direction) in a wide range.
Also, it is required in the projection screen that the displayed image light should be viewed in a high contrast. Also, it is necessary that a peripheral light other than the displayed image light should be reflected on the surface of the screen so as not disturb the observation and a shading layer 325 should be formed which is formed by a black stripe (BS) which corresponds to a non-light-condensing section in the cylindrical lens (that is, such as a non-transparent section for the image light) so as to have a smaller numerator in the above relationship.
As explained above, the double-surface lenticular sheet 320 is used for a projection television which is provided with a plurality of CRT projectors (in general, three sets such as R, G, and B).
On the other hand, there is a projection television which has only one set of projector (that is, a full-color display image is projected from a single lens) which is employs a method in which an LCD or a DMD is used for an optical engine section in the projector.
It is not necessary to compensate a color depositioned condition (color shift) of the image light for the R, G, and B in the screen for the projection-type projection television which has a single projector (which is called as a single-tube type). That is, it is acceptable only if the lens section which is formed by a cylindrical lens group should be disposed on a surface of the lens sheet because only emitting range (perspective angle) for the image light should be broadened (such a structure is called a single-surface lenticular sheet).
FIG. 11 is a view for explaining an example for a structure for a transparent screen which is used for a single-tube projection television.
Basically, the transparent screen formed by two members such as a lenticular sheet 370 and a fresnel lens sheet 360.
A lens section 71 is formed on only a surface of the lenticular sheet 370. Also, a shading layer 375 is formed on a plane surface on which the lens section 371 is not formed.
For a case of a screen which is provided with a single-surface lenticular sheet, it is required that the perspective angle should be enlarged in vertical direction as similarly to the above explained double-surface lenticular sheet.
FIG. 5 is a detailed view for an example of a structure for a conventional transparent screen which is used for a liquid crystal projection television etc. In the drawing, reference numeral 1 indicates a fresnel lens. The fresnel lens 1 is formed by disposing a lens layer 1b which has convex sections and concave sections on a surface of a plate base member layer 1a concentrically. Generally, the projector is disposed near the base member layer 1a in the liquid crystal projection television.
In addition, a lenticular sheet 2 is disposed near the lens layer 1b in the fresnel lens 1; thus, the transparent screen is formed by the fresnel lens 1 and the lenticular sheet 2.
For example, a structure of the lenticular sheet 2 is generally formed by a lenticular layer 3, a photo-sensitive resin layer 5, a shading layer 6, a bonding agent layer 7, and a dispersing layer 8 in which the lenticular layer 3 is disposed in the fresnel lens 1 and the dispersing layer 8 is disposed near the observing person. Here, a hard coat layer 9 is disposed on a surface of the dispersing layer 8 which is near the observing person according necessity so as to protect the surface.
The lenticular layer 3 is formed a plate base member layer 3a and a lens layer 3b which is disposed on its surface. The lens layer 3b is formed by disposing a plurality of half-cylindrical lenses 4 such that the longitudinal direction should be in parallel and a cylindrical surface 4a should be disposed near the fresnel lens 1.
Hereinafter, an example for a manufacturing operation for the structure of the lenticular sheet 2 is explained.
For manufacturing the lenticular layer 3, a lenticular layer 3b is formed by disposing a radiation curable resin under a non-hardened condition between a surface of the base member layer 3a and a mold (stamper) which has a reverse shape of the lens layer 3b, emitting a predetermined radiation from other surface of the base member layer 3a, and hardening the above resin. Also, the above lens layer 3b is bonded on the base member layer 3a; thus, a lenticular layer 3 is obtained.
Next, a photo-sensitive resin layer 5 is applied on a surface of the lenticular layer 3 near the base member layer 3a. 
For such a photo-sensitive resin layer 5, it is possible to name a member which has a characteristic in which it is adhesive under non-exposed condition and the adhesiveness disappears after being exposed and degenerated.
In addition, when a light is emitted from the lens array 3b via the fresnel lens 1 as similar to a case in which the transparent screen is used, a beam in a stripe manner is emitted so as to be condensed on the photo-sensitive resin layer 5 via the lenticular layer 3. In addition, the photo-sensitive resin layer 5 in a section which is exposed is denatured; thus the adhesiveness disappears. In addition, a transcription film which has a black transcription layer such as a black carbon is pressed on the photo-sensitive resin layer 5, the transcription layer is transcribed on an unexposed section which has an adhesiveness; thus, a shading layer 6 in a stripe manner in which a plurality of black lines are disposed is formed.
That is, a light is shaded by the shading layer 6 in a section through which the light does not transmit.
After that, plate dispersing layer 8 is further layered via a film adhesive layer 7 so as to be unified tightly; by doing this, a lenticular sheet 2 is obtained. Here, the dispersing layer 8 is formed by mixing a dispersing member which is formed by a plurality of glass beads in a matrix which is made of a plastic member such as an acrylic member.
In addition, a hard coat layer 9 is layered on a surface of the dispersing layer 8 according to necessity so as to be unified.
In addition, if the transparent screen is attached to a liquid crystal projector which is provided with a projector as shown in FIG. 5 and the light is emitted from the projector, the light becomes an approximate parallel light via the fresnel lens 1. In addition, a predetermined optical distribution angle is added by transmitting the light through the lenticular layer 3 such that the light disperses in a horizontal direction in the image appropriately; thus, the perspective angle is controlled in this direction. Here, the light which transmits through the lenticular layer 3 becomes a stripe light which is parallel with a longitudinal direction of the cylindrical lens. Furthermore, a light disperses in a vertical direction appropriately by the function of the dispersing layer 8 via the shading layer 6; thus, the perspective angle is controlled in this direction. Here, it is possible to improve S/N ration by the shading layer 6; thus, it is possible to provide an image which has a desirable contrast.
As explained above, a lenticular layer and a dispersing layer are used in a combined manner so as to control the perspective angle of the image in a horizontal direction and a vertical direction in a conventional lenticular sheet and a transparent screen. However, there have been problems such as a reduced gain (brightness) which is caused by a light absorption in the dispersing layer and a reduced S/N ration caused by the increase in a white dispersion.
Also, a method can be provided for controlling the perspective angle in the horizontal direction and the vertical direction by disposing the cylindrical lenses such that each longitudinal direction should be orthogonal to each other on both sides when two pieces of lenticular sheets are overlapped such that each longitudinal direction should be orthogonal to each other or a plurality of the cylindrical lenses are disposed on both surfaces of a base member layer.
However, in the former case, it is necessary to control the relationship of two lenticular sheets strictly so as to maintain the optical characteristics in two lenticular sheets. Also, it is necessary to form a lens in a fine forming operations under condition that it is necessary to used the material member for forming the cylindrical lens twice as many as the conventional case substantially; therefore, there has been a problem that the cost for the material member and the cost for forming the material member are expensive.
In a latter case, the cylindrical lens groups of which disposition direction are different from each other must be formed on both surfaces of one piece of the base material layer. Therefore, as similarly, it is necessary to perform the forming operations for the lens section twice.
Furthermore, there is a method in which a plurality of independent lenses or prisms which can add the distribution angle in both the vertical direction and the horizontal direction are disposed on a surface of the base member layer as similar to a micro-lens array. However, it is necessary to perform a complicate forming operation and it is difficult to increase an area and perform a fine pitch operation. Also, productivity is low. Therefore, the cost increases inevitably.
Furthermore, in Japanese Unexamined Patent Application, First Publication No. Hei 9-311203, a lenticular lens sheet is disclosed is disclosed which forms a lens plate in which a plurality of lenticular lens elements (cylindrical lenses) which have lenticular lens shape on incident surface and fine lenticular lens shapes which are formed by a molding operation so as to be orthogonal with each other along surfaces of the cylindrical lenses.
As explained above, there is a problem to be solved in the transparent projection television for enlarging the perspective angle in the vertical direction and improving the contrast.
A dispersing layer which is formed by dispersing the optical dispersing particle and lenticular layer are used in a combined manner so as to control the perspective angle of the image in a horizontal direction and a vertical direction in a conventional lenticular sheet and a transparent screen.
However, in the above optical dispersing layer, if an optical dispersing agent (particle) is used excessively, there have been problems in that a gain (brightness) is reduced by an optical absorption and an S/N ration is reduced by an increase in a white dispersion.
Also, a diameter of a projection pupil in a projection lens is small in the transparent projection television which is provided with a liquid crystal projector. Therefore, as compared with a CRT transparent projection television, there have been inherent problems in that the brightness of the incident light from the projector is partially high (hot spot), the cylindrical lens may be observed to be bright in a stripe manner in a disposing direction (hot bar), and an unnecessary scintillation which is observed in a projection image may occur frequently.
Furthermore, it is not possible to solve these problems sufficiently only by enlarging the perspective angle in the vertical direction, a hot spot, a hot bar, and a scintillation by enhancing the optical dispersion characteristics by using an optical dispersing agent (particle). That is, it is newly required to add a dispersion angle by a lens function.